Post Translational Modification: Lecture 2 Flashcards
What cellular events is PTM involved in? (6)
gene expression
signal transduction
cell-cell interaction
protein-protein interaction
communication between intra and extracellular environment
What is trasncriptome?
whole mass of mrna transcripts in the body
what is PTM?
Covalent addition to or cleavage of proteins
After/ during biosynthesis
important in cell signalling
occurs on amino acid chains or at a terminal
What is proteome?
total mass of proteins in body- roughly 1 million
How are there more proteins than genes?
splicing process and PTM
what are the 3 types of germ layers that cells can differentiate into?
Endoderm- internal layer e.g. lung, thyroid, pancreatic cell
Mesoderm- middle layer e.g. cardiac, rbc, smooth muscle gut, skeletal muscle
Ectoderm- outer layer e.g. skin cells, neurone brain, pigment cells.
how does PTM relate to proteome?
PTM increase diversity of proteome whilst extending function and stability- because it affects the longevity as well as activity of protein.
Types of PTM to a protein? (5)
Glycosylation
Phosphorylation
Disulfide bond
Methylation
Acetylation
summary of glycosylation?
attach sugar- usually to N or O in amino acid side chain
summary of methylation?
add methyl group- usually at lysine or arginine residues
summary of acetylation?
add acetyl group to N-terminus of protein or at lysine residues
summary of disulfide bond?
covalent bond of S at two cysteine residues
summary of phosphorylation?
Add phosphate to serine, threonine or tyrosine
genres of PTM? (4)
cleavage- proteolysis
complex molecules- glycosylation
chemical- acetylation, methylation, phosphorylation
proteins/peptides- ubiquitylation, sumoylation
example of cleavage PTM in cell?
Insulin production. Unwanted parts of the peptide removed after translation and translocation and folding. It gets PMT with disulfide bonds (signal peptide) and then gets exported to Golgi where it’s cleaved
Whats the point of adding functional groups as PMT?
enable cell signalling and cell can react specifically and rapidly to events like environmental conditions. Fast bc can just activate/inactivate protein for rapid response e.g. insulin
key points of effects of phosphorylation? (4)
- Reversible addition/removal
- Phosphate from hydrolysis of ATP to ADP
- Cause conformational change bc phosphate -2 charge. Cause charge disparity in amino acids and change structure
- Can activate (open up/reveal active site) or deactivate (mask binding site)
2 ways phosphate can be added/taken away?
protein kinase and phosphatase
What does protein kinase do?
catalyse transfer of phosphate from high energy donor to specific substrate phosphorylation
what is kinome?
whole family of 513 kinases- 35 atypical catalytical domain, 478 homologous domain
what does phosphatase do and key points about it? (4)
catalyses dephosphorylation- removal of phosphate from substrate by hydrolysing monoesters into phosphate ion and molecule with free hydroxyl group
Broad range or specific
broad range controlled by regulatory proteins
often in chain-cell signalling
Steps of phosphorylation in regulating glycogen breakdown?
- epinephrine bind receptor
- activates adenylyl cyclase
- adenylyl cyclase convert atp to cAMP
- cAMP activate cAMP-dependant protein kinase
- this activates phosphorylase kinase by phosphorylation
- this activates glycogen phosphorylase by phosphorylation
- converts glycogen to glucose-1-phosphate
What is definition of glycosylation?
carbohydrate (monomer to complex) covalently bound to functional group e.g. hydroxyl on protein by glycosidic bond
Functions of glycosylation? (6)
- correct folding
- increase protein stability- secreted proteins
- cell/cell or cell/environment adhesion
- immune response
- hormone activity
- embryonic development
what is the molecule which anchors carbohydrate to the membrane?
Dolichol
Whats the process of dolichol, glycosylation and golgi?
membrane of ER have dolichol with phosphate on the side of cytosol. Then carbs added.
Then flipase flips it so its on the lumen side.
Simultaneously, ribosome translating mrna and folding
Glycosyl transferase attach the carb structure to the polypeptide
Gets transferred to golgi where gets modified- n-linked or o-linked glycosylation
what are all the types of places glycosylation can get linked?
N-linked
O-linked
C-linked
Glypiation
Phosphoglycosylation
Bond, location example of N-linked?
Glycan bind to amino group on asparagine
endoplasmic reticulum
insulin receptor, ecm, regulation
bond, location, example O -linked?
monosaccharides bind to hydroxyl group serine/threonine
ER, golgi, cytosol
collagen, pathogenic bacteria e.g. clostridium toxins
Bond, loaction example Glypiation?
glycan core links a phospholipid and protein
plasma membrane?
anchors cell surface proteins
bond of C-linked?
Mannose binds to indole ring of tryptophan
Main points of acetylation? (4)
addition/removal of acetyl group (CO-CH3)
donated by Ac-CoA
co or post translational
80-90% co translational at N-terminal of polypeptide
what are the 2 types of acetylation?
N- terminal:
*co-translational modification eukaryotes
*synthesis localisation stability
*80-90% proteins
Lysine acetylation:
*acetylation /deacetylation linked to transcription factors
*activation of gene expression
what is NAT and what it do?
N-terminal acetyltransferases- catalyses n terminal acetylation
transfer acetyl group from coA to the alpha amino group on the first amino acid residue of polypeptide chain
how does histone modification work and what controls it?
histone acetylation- controlled by HAT/ KAT (histone/lysine acetyltransferase). Relaxes chromatin structure.
histone deacetylation- controlled by HDAC/KDAC (histone/lysine deacetylase) remove acetyl group and DNA get more tighter, reduce gene expression
How does acetylation of histone increase transcription?
removes positive charge from the histone, encourage binding of effector proteins and relaxation of chromatin
Therapeutic applications of acetylation? (3)
- targeting HDAC in malignant cells- because these are in charge of reducing gene expression
- HDI- small molecule inhibitors
- T cell lymphoma targeted by issuberoylinine hydroxamic acids
Methylation and key points? (3)
addition of methyl group CH2- changes activity of protein
lysine- 3 times methyl can be transferred
arginine- 2 times methyl transferred
key points of lysine methylation? (4)
activation/suppression
reversed with demethylase
histone function regulation
epigenetic regulation of transcription
What is KMT?
lysine methyltransferase. Donates the methyl group from S-adenosylmethionine
difference between carbonyl and nitrogen methylation?
carbonyl- reversible and used to modulate reaction
nitrogen- irreversible and used to create new amino
Key points of arginine methylation? (5)
regulating RNA processing
gene transcription
DNA damage repair
protein translocation
signal transduction
what’s p53 got to do with PMT? (4)
- p53 activity controlled by acetylation, phosphorylation, methylation
- concentrated in N and C terminals
- acetylation increase p53 stability- increase dna interaction
- under stress, upregulation of kinase activity- reduce p53 activity and increase cofactor activity
